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    <title>Document</title>
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    <h1>计算结果</h1>
    <form oninput="res.value = num1.valueAsNumber*num2.valueAsNumber">
      <input type="number" id="num1" />*<input type="number" id="num2" /> =
      <output for="num1 num2" name="res" />
    </form>
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